1. |
- Hemphälä, Hillevi, et al.
(författare)
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A method for risk assessment within Visual Ergonomics
- 2015
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Ingår i: Proceedings of the 19th Triennial Congress of the International Ergonomics Association. ; , s. nr 1203-
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Konferensbidrag (refereegranskat)abstract
- IntroductionInsufficient visual ability can lead to increased work load and contribute to eyestrain and musculoskeletal discomfort, since “the eye leads the body” (Anshel, 2005). It has been shown that visually demanding work, such as computer work, is associated with eye discomfort, headaches and muscle pains in mainly the neck and shoulders (Rosenfield, 2011).Although the relation between eyestrain and musculoskeletal discomfort is not fully understood, studies have shown that straining the eyes increases the musculoskeletal activity in neck and shoulders (trapezius), and an association between visually demanding work, eye problems, headache and/or muscle problems have been found (Aarås et al., 2001; IESNA, 2011, Richter et al., 2008; Zetterberg et al., 2013). Problems due to insufficient visual ergonomics not only exist in computer intensive jobs, but in other professions as well. For example, surgeons and other surgical personnel that report eyestrain also report twice as much musculoskeletal discomfort from the upper part of the body (Hemphälä et al., 2011). In an intervention study among postmen, both eyestrain and musculoskeletal discomfort decreased after a visual ergonomic intervention. The intervention included providing customized eyeglasses and optimal lighting conditions (Hemphälä et al., 2012). Apart from health and well-being being affected by a poor visual ergonomic work environment, quality and productivity may also be reduced (Eklund, 2009).The aim of this paper is to present the first version of a practical, easy-to-use, and time-efficient risk assessment method for visual ergonomics. The development of the method including the evaluation will also be described. With such a method, risk factors within the visual environment can hopefully be detected, and interventions implemented in order to reduce the prevalence of symptoms related to poor visual ergonomics among workers.MethodsA first version of the method has been developed, mainly based on existing checklists and instruments (Colon et al. 1999; Børsting et al., 2008, Knave et al., 1985, Sheedy and Shaw-McMinn, 2002; Wilson & Corlett, 2005). During spring 2015, 30 ergonomists will be updated about visual ergonomics and introduced to the risk assessment method. Each ergonomist will thereafter use the method in 10 workplaces, yielding data and practical experiences from 300 risk assessments. These data will then be used to test the validity and reliability of the method, and if necessary to further develop it.ResultsThe first version of the risk assessment method for Visual Ergonomics will be presented at IEA 2015, together with results from the approximately 300 risk assessments made by the ergonomists. So far, the factors included in the method are objective measurements such as illuminance, luminance contrast, uniformity values, expert assessment of the risk for glare, and subjective ratings of the visual ability, eyestrain and musculoskeletal discomfort.DiscussionThe presented method will be compared to other similar methods. The used method for development will be discussed in relation to validity and reliability. Finally the presented risk assessment method will be discussed in relation to usefulness in prevention of discomfort and work related disorders at work places.
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2. |
- Glimne, Susanne, et al.
(författare)
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Headaches in combination with visual ability, eye- and musculoskeletal strain in connection with visually demanding work tasks
- 2022
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Konferensbidrag (refereegranskat)abstract
- Suboptimal visual ergonomics (i.e., the interaction between our vision, the light, the visual object, and the influence of other factors which impairs visibility) in work environment such as glare can cause headache in combination with eyestrain, visual ability, and musculoskeletal strain. Symptoms constituted to the syndrome of eyestrain has been well described among computer workers (see for example Han et al., 2013; Portello et al., 2012; Bhanderi et al., 2008; Mocci et al., 2001; Sanchez-Roman et al., 1996). However, research has not focused on investigating the presence of headaches associated with eye-related and musculoskeletal disorders among employees and visual related environmental factors.The purpose of presented research was to study the presence of headaches in combination with visual ability, eye- and musculoskeletal strain, and work ability in connection with visually demanding work. Trained assessors recruited study participants primarily from their regular clients in the OHS field. Evaluators were instructed to recruit participants with a variety of characteristics to ensure highly variable data, such as different work tasks, age, and gender. The participants mean age was 48.3 years (±10.3); 66% were women.A visual ergonomics risk assessment method (VERAM, Heiden et al. 2019; Zetterberg et al. 2017) was used to compile the participated workers subjective grading of headache, eye- and musculoskeletal strain using a questionnaire (n=430). At the same time, an evaluation of the visual environment was carried out, which established if there was a risk of glare associated with the implementation of work task (e.g., computer work and other related work such as industry, healthcare, and shipping industry). The frequency of headaches was divided into three categories; (1) no headache, (2) headache occasionally, and (3) headache a few times per week/almost every day. The measurements regarding evaluation of the visual environment used a photometer, an instrument which was available and that the assessors could use, usually a Hagner ScreenMaster or Hagner S1 / S2 / S3.About 65% of the workers reported headaches occasionally, a few times/week or almost every day. Among the workers with headaches reported about 29% of them that they experienced the headaches a few times/week or almost every day.Out of the workers with headaches reported 37% a severity of the headaches of more than 3 (on a scale of 1-10) and 5 % reported a severity of more than 6. About 40% of the workers also stated that the headaches affected their working ability. The headaches were mainly located around the eyes, forehead, or temples (70%) and came in the afternoon (69%). About 75% of the workers also reported that the headache disappeared or were reduced when they were off work for one night or over the weekend. The data collection showed that visual- related symptoms increased the higher the estimated headaches was.The musculoskeletal strain increased when the headache increased. When workers reported a high frequency of headaches 95% of them reported neck strain, 86% shoulder strain, 73% upper back strain, and 61% were reported arm strain.Moreover, only 8.2% of the workers rated their visual ability as bad or very bad, but at the same time, about 60% reported dim vision, 14% diplopia, and 59% problems changing focus at some time.Dividing the data into workers with experienced or unexperienced headaches this study has shown that there was a significant presence of headaches in combination with visual related symptoms regarding experienced photophobia (p=0.011), eye pain (p=0.015), diplopia (p=0.029), and arm strain (p=0.006). Further, the statistical analysis showed that there was a tendency of combination regarding headaches and visual ability (p=0.070).Dividing the data into workers with experienced or unexperienced headaches, our study showed that the frequency of headache increased due to high luminance levels within the visual field (p=0.044).This study concludes presence of headaches in combination with eye- and musculoskeletal strain performing work task such as computer work. Further, the presence of headaches is due to visual ability induced by high luminance levels within the visual field.
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3. |
- Heiden, Marina, 1974-, et al.
(författare)
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Validity of a computer-based risk assessment method for visual ergonomics
- 2019
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Ingår i: International Journal of Industrial Ergonomics. - : Elsevier BV. - 0169-8141 .- 1872-8219. ; 72, s. 180-187
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Tidskriftsartikel (refereegranskat)abstract
- ObjectiveTo describe the development of a computer-based risk assessment method for visual ergonomics, and assess its face validity, content validity, and internal consistency.MethodsThe risk assessment method contained a questionnaire for the worker, an evaluation form for the evaluator, a section of follow-up questions based on the worker's responses, and a section for recommended changes, including an overall risk assessment with respect to daylight, lighting, illuminance, glare, flicker, work space, work object and work postures, respectively. Forty-eight trained evaluators used the method to perform 224 workplace evaluations. Content validity of the method was assessed by the completeness and distribution of responses, and internal consistency was assessed by Cronbach's alpha, Spearman's rank correlation between items and indices, and exploratory factor analysis.ResultsThe proportion of missing values in items was generally low (questionnaire: 0–2.3%; evaluation form: 1.4–4.1%). In the questionnaire, items about double vision, migraine and corrective lenses had limited information content. Cronbach's alpha and item-index correlations for the indices frequency of eyestrain, intensity of eyestrain, visual symptoms, lighting conditions, frequency of musculoskeletal discomfort and intensity of musculoskeletal discomfort were satisfactory. Based on the factor analysis, suggestions for improving some of the indices were made.ConclusionOur findings suggest that this computer-based method is a valid instrument for assessing risks in the visual work environment. By incorporating subjective ratings by the worker as well as objective measurements of the work environment, it provides a good basis for recommendations with respect to daylight, lighting, work surfaces/material, and work object.Relevance to industryVisual environment factors, such as glare, can cause eyestrain, headache and musculoskeletal discomfort. This method satisfies the need of a valid tool for determining risks associated with the visual work environment. It contains both worker's ratings and objective measurements, and is designed to be used in different types of work.
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4. |
- Hemphälä, Hillevi, et al.
(författare)
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A method for assessing risks in visual ergonomics
- 2015
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Ingår i: Creating Sustainable Work-environments. - : NEHF. - 9788299574754 ; , s. B1-1-
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- IntroductionA method for risk assessment in the field of visual ergonomics is under development. Insufficient visual ability can lead to increased workload and contribute to eyestrain and musculoskeletal discomfort. Although the relation between eyestrain and musculoskeletal discomfort is not fully understood, studies have shown that straining the eyes increases the musculoskeletal activity in the neck and shoulders (trapezius); associations between visually demanding work, eye problems, headaches and/or muscle problems have also been found (Aarås et al., 2001; IESNA, 2011; Zetterlund et al., 2009; Zetterberg et al., 2013; Toomingas et al., 2013; Richter et al., 2011; Richter et al., 2015). Problems due to insufficient visual ergonomics not only exist in computer intensive work, but in other professions as well, such as surgeons and postal workers (Hemphälä et al., 2011; Hemphälä et al.,2012).The aim of this project is to develop a practical, easy-to-use, and time efficient risk assessment method for visual ergonomics. With this method, risk factors in the visual environment can be detected, and interventions implemented to reduce the prevalence of symptoms related to poor visual ergonomics among workers.MethodsA first version of the risk assessment method has already been developed. In the spring of 2015, 27 ergonomists were taught visual ergonomics and introduced to the method. After the course, each ergonomist used the method to assess 8-10 workplaces, providing data and practical experiences from approximately 250 risk assessments. These data will be used to further develop and improve the method. During the fall of 2015 and spring of 2016, two other groups, each consisting of 30 ergonomists, will be trained in using the revised version of the risk assessment method in approximately 10 workplaces each. Data from these assessments will be used to test the validity and reliability of the method.ResultsThe first version of the risk assessment method for visual ergonomics will be presented at NES 2015 together with the results from the approximately 250 risk assessments made by the first group of ergonomists. So far, the factors included in the method are objective measurements of illuminance, luminance contrast, illuminance uniformity values, size of work object, visual angle; expert assessment of the risk for glare; and subjective ratings of visual ability, eyestrain and musculoskeletal discomfort. Some tendencies have been found of correlations between an objectively-rated high risk for glare and eyestrain/headache, as well as between a high contrast glare/luminance ratio and eyestrain.ConclusionSeveral factors in the visual environment contribute to wellbeing and the level of performance. In this risk assessment method for visual ergonomics, ergonomists have been trained to evaluate, for example, the risk for glare, as one of the major risks. The risk assessment method presented will be discussed in relation to its usefulness in the prevention of discomfort and work-related disorders at workplaces.
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5. |
- Hemphälä, H, et al.
(författare)
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A method for assessing risks in visual ergonomics
- 2015
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Ingår i: Proceedings of Nordic Ergonomics Society 47th Annual Conference. - 9788299574754
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Konferensbidrag (refereegranskat)abstract
- A method for risk assessment in the field of visual ergonomics is under development. Insufficient visual ability can lead to increased workload and contribute to eyestrain and musculoskeletal discomfort. Although the relation between eyestrain and musculoskeletal discomfort is not fully understood, studies have shown that straining the eyes increases the musculoskeletal activity in the neck and shoulders (trapezius); associations between visually demanding work, eye problems, headaches and/or muscle problems have also been found (Aarås et al., 2001; IESNA, 2011; Zetterlund et al., 2009; Zetterberg et al., 2013; Toomingas et al., 2013; Richter et al., 2011; Richter et al., 2015). Problems due to insufficient visual ergonomics not only exist in computer intensive work, but in other professions as well, such as surgeons and postal workers (Hemphälä et al., 2011; Hemphälä et al., 2012). The aim of this project is to develop a practical, easy-to-use, and time efficient risk assessment method for visual ergonomics. With this method, risk factors in the visual environment can be detected, and interventions implemented to reduce the prevalence of symptoms related to poor visual ergonomics among workers.
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6. |
- Hemphälä, Hillevi, et al.
(författare)
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A method for assessing risks within visual ergonomics
- 2014
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Ingår i: 11th International Symposium on Human Factors in Organisational Design and Management & 46th Annual Nordic Ergonomics Society Conference. - Santa Monica, CA, USA : The IEA PRESS. - 9788793130135 ; , s. 111-112
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Konferensbidrag (refereegranskat)abstract
- 1. IntroductionInsufficient visual ability can lead to strained work load for employees and can contribute to eyestrain and musculoskeletal discomfort, “the eye leads the body” (Anshel, 2005). An optimal visual environment provides physical conditions for work in the best possible way. Visually demanding work, such as computer work, is associated with eye discomfort, headaches and muscle pains in mainly the neck and shoulders (Rosenfield, 2011). For computer workers in North America studies show that 75-90 % of the workers reported subjective symptoms from the eyes (Anshel, 2005). The causality between eyestrain and musculoskeletal discomfort is not fully understood, but studies have shown that straining the eyes increases the musculoskeletal activity in neck and shoulders (trapezius), and a link between visually demanding work, eye problems, headache and/or muscle problems have been found (Aarås et al., 2001; Richter et al., 2008; Zetterlund et al., 2009; Zetterberg et al., 2013). A study of call-center workers in Sweden showed that 21% of workers have both eyes and neck problems (Wiholm et al., 2007). Ergonomic problems also exist for professions where computer work is not dominant. Surgeons and other surgical personnel, with subjective eye discomfort, reported twice the incidence of musculoskeletal disorders when compared with staff without eye symptoms (Hemphälä et al., 2011). In an intervention study among postmen the eyestrain and musculoskeletal discomfort decreased after visual ergonomic interventions including customized eyeglasses and optimal lighting conditions (Hemphälä et al., 2012). Apart from health and well-being being affected by a poor visual ergonomic work environment, the quality and productivity are also involved (Eklund, 2009).Lighting is an important factor; both the lighting quantity (strength) and quality (e.g. light distribution, direction, glare and contrast). Too low illumination makes it difficult to see clearly and may thus lower performance, high illuminance can cause glare and lead to increased eye fatigue and decreased productivity (IESNA, 2011).2. MethodsThere are several factors to consider when developing a method for visual ergonomics risk assessment of subjective symptoms and discomfort of the eyes (Colon et al. 1999; Børsting et al., 2008, Knave et al., 1985). There are also checklists used in eye exams or medical appointments (Sheedy and Shaw-McMinn, 2002; Wilson & Corlett, 2005). These will be used as basis in the presents the project intended to develop a risk assessment instrument for visual ergonomics.3. ResultsA preliminary version of a risk analysis method for Visual Ergonomics has been developed and will be presented, with a focus on discussing with the audience which factors should primarily be included. The factors included so far in the method are the objective measurements such as illuminance, luminance contrast, uniformity values, expert assessment of the risk for glare; indirect measurements such as subjective ratings of the visual ability, eyestrain and musculoskeletal discomfort. The goal is to develop a practical time efficient method that is easy to use. With such a tool, actions needed to reduce the visual load among the workers, the companies and the society’s negative consequences induced by work-related eyestrain and musculoskeletal discomfort can hopefully be identified.
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7. |
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8. |
- Hemphälä, Hillevi, et al.
(författare)
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A risk assessment method for visual ergonomics
- 2016
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Ingår i: NES2016 - ERGONOMICS IN THEORY AND PRACTICE - Proceedings of 48th Annual Conference of Nordic Ergonomics and Human Factors Society. - Kuopio : School of Medicine , Faculty of Health Sciences : University of Eastern Finland. - 9789526121925
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Konferensbidrag (refereegranskat)abstract
- The visual environment can affect our wellbeing in many ways. Insufficient visual ability can lead to increased workload and contribute to eyestrain and musculoskeletal discomfort that in turn could lead to sick leave. Non-visual effects, such as flicker from luminaires can cause eyestrain or headache/migraine. Glare from luminaires or windows within the visual field can cause disability glare or discomfort glare. Glare while performing computer tasks causes visual fatigue and leads to strabismus measured with fixation disparity (harder for the eyes to focus). Strabismus leads to eyestrain, and eyestrain can lead to musculoskeletal discomfort.Although the relation between eyestrain and musculoskeletal discomfort is not fully understood, studies have shown that straining the eyes increases the musculoskeletal activity in the neck and shoulders (muscle trapezius); associations between visually demanding work, eye problems, headaches and/or muscle problems have also been found.The aim of this project is to develop a practical, easy-to-use, and time efficient risk assessment method for visual ergonomics. With this method, risk factors in the visualenvironment can be detected, and interventions implemented to reduce the prevalence of symptoms related to poor visual ergonomics among workers.The developed visual ergonomics risk analysis method has been used at several work places by ergonomists that have been educated in visual ergonomics. The results from the subjective part of the method show that many individuals report eyestrain and headache. This can be caused by many different factors such as wrong power in lenses, glare, flickering lights etc. Therefore it is essential that if you have a visually demanding work (such as computer work) you have to do eye examinations every other year to make sure that your vision is at its best. But the lighting situation at workplaces is also a key factor to consider in a good visual environment, to increase the level of performance. To increase wellbeing at work and reduce sick leave the visual environment needs to be good, with sufficient illuminance, a good luminance ratio, no glare from luminaires or windows,no flicker, and a good visibility of the work task. Education in risk analysis of the visual environment is essential for many different occupations such as lighting designers, ergonomists, working life inspectors, optometrists, to ensure a better understanding of the impact on wellbeing that the visual environment have.The researchers behind this study will have a finished visual ergonomics risk analysis method by the year of 2017.
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9. |
- Hemphälä, Hillevi, et al.
(författare)
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Objective risk assessment of glare and subjective rating of the frequency of glare ‐ a visual ergonomics risk assessment, VERAM
- 2022
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Konferensbidrag (refereegranskat)abstract
- Insufficient lighting conditions and glare from luminaires in the visual environment can affect our visual ability and cause eyestrain, headache, and musculoskeletal strain. Knave et al. found that the frequency of reported glare was associated with more eyestrain. In this study a subjectively rated frequency of glare was compared to an objectively rated risk for glare made by trained assessors.A visual ergonomics risk assessment method (VERAM) was used to gather data at workplaces, mainly computer workstations (n=420). Trained assessors (ergonomists) measured the luminance ratio and assessed the risk for glare (objective risk for glare) divided into three categories high risk (red), low risk (yellow) and no risk (green).Workers rated the frequency of experienced glare at their workplaces (subjective assessment of glare) via questionnaires. The frequency of subjective strain was divided into three categories; no, never; occasionally; a few times a week/almost always.Workers rated the frequency of glare present more seldom than the trained assessors rated the presence for risk for glare, at the same workplaces. One factor behind this might be individuals’ ability to evaluate the visual environment such as risk for glare. A trained assessor can easier evaluate any risks in the visual environment.When the objective risk for glare was assessed to be high (red) or low (yellow) the percentage of individuals reporting strain, such as eyestrain and musculoskeletal strain, increased for most symptoms compared to when there was no risk (green). An objective risk assessment for glare needs to be performed together with a subjective rating of the frequency of glare to find the individuals with problems.
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10. |
- Hemphälä, Hillevi, et al.
(författare)
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Risks in the visual environment such as glare, illuminance, and luminance ratio - risk assessments made with visual ergonomics risk assessment method - VERAM - a descriptive paper
- 2021
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Ingår i: Proceedings of the Conference CIE 2021 : September 27 - 29, 2021 hosted by the CIE National Committee (NC) Malaysia online - September 27 - 29, 2021 hosted by the CIE National Committee (NC) Malaysia online. - 9783902842299
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Konferensbidrag (refereegranskat)abstract
- The visual environment has an impact on subjective strain and headaches. A visual ergonomics risk assessment method, VERAM, was used on 217 workplaces, and consists of both of a subjective questionnaire and an objective risk assessment, the objective risks are presented in this paper. The risk for daylight was assessed to be yellow (risk) or red (high risk) at 53% of the workplaces and the risk for glare was yellow or red at 66%. The assessment of the lighting design showed a yellow or red risk at 44% of the workplaces and the illuminance was assessed to be insufficient at 49% of the workplaces. Flicker or TLM (temporal light modulation) was assessed to be a problem among 33%. These results show that the design of the visual environment is in most cases not performed in a satisfying way. To increase wellbeing, health and performance a good visual environment is essential.
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11. |
- Hemphälä, Hillevi, et al.
(författare)
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Visual Symptoms and Risk Assessment Using Visual Ergonomics Risk Assessment Method (VERAM)
- 2021
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Ingår i: Proceedings of the 21st Congress of the International Ergonomics Association (IEA 2021) - Volume II : Inclusive Design - Inclusive Design. - Cham : Springer International Publishing. - 2367-3389 .- 2367-3370. - 9783030746049 ; 220, s. 729-735, s. 729-735
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Konferensbidrag (refereegranskat)abstract
- A visual environment impaired by e.g. glare can cause eyestrain, visual symptoms and musculoskeletal strain. A Visual Ergonomics Risk Assessment Method (VERAM) consisting of both a subjective questionnaire and an objective risk assessment, have been used at 217 workplaces, mainly computer work. VERAM can be used to examine and prevent deficiencies and increase wellbeing as well as detecting risks in the visual work environment and suggest measures that can be used to reduce the risks. The questionnaire showed that eyestrain, visual symptoms and musculoskeletal strain are common among Swedish workers. The overall risk assessments for glare and amount of illuminance on work surface are divided into three categories, green – no risk, yellow – risk, and red – high risk. Risk of glare and insufficient illuminance was present at 66% and 49% of the assessed workplaces, respectively. When the risk of glare and illuminance levels was rated as red, the frequency of the subjective strain was higher.
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12. |
- Hämphälä, Hillevi, et al.
(författare)
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A risk assessment method for visual ergonomics, VERAM
- 2017
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Konferensbidrag (refereegranskat)abstract
- A valid, reliable, practical and easy-to-use risk assessment method for visual ergonomics named VERAM (Visual Ergonomics Risk Analysis Method) has been developed. With this method, risk factors in the visual environment can be detected, and interventions implemented to reduce the prevalence of symptoms related to poor visual ergonomics among workers can be evaluated.The visual environment can affect our wellbeing in many ways. Glare from luminaires or windows within the visual field can cause disability glare or discomfort glare. Glare while performing computer tasks causes visual fatigue and leads to strabismus measured with fixation disparity (harder for the eyes to focus). Strabismus leads to eyestrain, and eyestrain can lead to musculoskeletal discomfort. Non-visual effects, such as flicker from luminaires can cause eyestrain or headache/migraine. Insufficient visual ability can lead to increased workload and contribute to eyestrain and musculoskeletal discomfort that in turn could lead to sick leave. As human beings, we need daylight to get a normal circadian rhythm. The visual environment needs to be designed to allow daylight entering, but have a possibility to prevent disturbing daylight.No method for evaluating the visual environment together with the individual’s subjective strain has previously existed. Personnel from occupational health departments (75 individuals) have used the developed visual ergonomics risk analysis method at several work places. Before using the method they were given a course in visual ergonomics and taught how to use the method.VERAM consists of two main parts. The first part is a subjective questionnaire with questions regarding the individual’s problem such as eyestrain and headache, but also their rating of the visual environment.The second objective part is performed by the assessors and consists of:measuring the illuminance and luminancerating of the visual environment and different risks (risk for glare, flicker, work task, daylight, work posture etc.)Feedback from the subjective part, the light measurements and the ratingsRecommendationsTo increase wellbeing at work and reduce sick leave, the visual environment needs to be good. This includes sufficient illuminance, a good luminance ratio, no glare from luminaires or windows, no flicker, and a good visibility of the work task. Education in risk analysis of the visual environment is essential for many different occupations such as lighting designers, ergonomists, working life inspectors, optometrists, to ensure a better understanding of the impact on wellbeing that the visual environment have. The main purposes of this study is to develop a visual environment risk analysis method and to increase the awareness and knowledge visual ergonomics.
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13. |
- Nylén, Anders, et al.
(författare)
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Control Design Based on FMI: A Diesel Engine Control Case Study
- 2016
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Ingår i: 8th IFAC Symposium on Advances in Automotive Control AAC 2016. - : Elsevier BV. ; 49:11, s. 231-238
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Konferensbidrag (refereegranskat)abstract
- Modelica allows systems to be described with reuseable components and with a high precision. To be able to use such complex models efficiently, high demands are set on tools that allow the user to extract the information needed from the models in a straight-forward manner. For this purpose, design-of-experiments techniques can be used to systematically analyze the complex models.In this paper, it is demonstrated how a Modelica model of a diesel engine can be used for control design. The engine model has multiple inputs and outputs, it is nonlinear, has many parameters, and has a higher order than most control design algorithms are able to handle in a numerically robust way.It is shown how the features for dynamic design-of-experiments analysis in the FMI Toolbox for MATLAB can be used to analyze the variation in system dynamics across the engine operating range. A gain scheduling of nine multivariable linear-quadratic-gaussian (LQG) controllers, is designed based on linearization and model reduction of the original nonlinear FMU model.
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14. |
- Zetterberg, Camilla, PhD, 1970-, et al.
(författare)
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Intra-rater reliability of the Visual Ergonomics Risk Assessment Method (VERAM)
- 2018
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Konferensbidrag (refereegranskat)abstract
- Introduction: Visually demanding near work can cause eye discomfort, and eye and neck/shoulder discomfort during, e.g., computer work are associated. Apart from visual demands and dryness a number of environmental factors including design of the work station, lighting, glare, and the quality of the computer screen might exert an impact on eye-related symptoms. To date, there is a lack of valid and reliable instruments assessing factors associated with eye- or visual symptoms. Therefore, a new method to assess visual ergonomics at workplaces was developed in Sweden between 2014 and 2016, the Visual Ergonomics Risk Assessment Method - VERAM. A first version of the method was drafted by the researchers mainly from existing checklists and instruments, and tested in the field by trained visual ergonomists. The method was then revised and used in the field to collect data for validity and reliability analyses. The final version of VERAM includes both a questionnaire for the employee, and an expert evaluation of the employee’s workplace. The questionnaire consists of subjective ratings in six domains: eye discomfort (frequency and intensity), musculoskeletal discomfort (frequency and intensity), ratings of visual symptoms (e.g. blurred and double vision) and ratings of the visual environment (e.g. illumination levels, glare and reflexes from a work object or a computer screen). The expert evaluation consists of both objective measurements and subjective assessments resulting in an overall expert risk assessment (no risk, low risk or high risk) of eight factors: daylight, lighting, illuminance, glare, flicker, work space, work object and work posture.Aim: At the IEA conference 2018 the new VERAM method will be presented together with results from intra-rater reliability analyses.Results: Intra-rater reliability was evaluated with a re-test interval of minimum two and maximum three weeks. 99 employees were included in the analyses and 32 visual ergonomists performed the corresponding expert evaluations. The Intraclass Correlations (ICC) were between 0.70 and 0.87 for the six subjective domains, and there were no significant systematic differences between the first and second rating for any of the subjective domains (rmANOVA, p > 0.05, α = 0.008). For the eight environmental factors the expert estimated the risk equally during the first and the second assessment in 69-92% of the cases, and, as seen for the subjective domains, there were no significant systematic differences for any of the eight factors (Wilcoxon sign rank test, p > 0.014, α = 0.006). To control for multiple comparisons the Bonferroni method was used.Conclusion: The Visual Ergonomics Risk Assessment Method – VERAM showed good intra-rater reliability, both for the subjective questionnaire for the employee, and for the expert evaluation of the employee’s workplace when performed by a trained visual ergonomist.
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15. |
- Zetterberg, Camilla, PhD, 1970-, et al.
(författare)
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Reliability of a new risk assessment method for visual ergonomics
- 2019
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Ingår i: International Journal of Industrial Ergonomics. - : Elsevier BV. - 0169-8141 .- 1872-8219. ; 72, s. 71-79
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Tidskriftsartikel (refereegranskat)abstract
- IntroductionThe Visual Ergonomics Risk Assessment Method (VERAM) is a newly developed and validated method to assess visual ergonomics at workplaces. VERAM consists of a questionnaire and an objective evaluation.ObjectiveTo evaluate reliability of VERAM by assessing test-retest reliability of the questionnaire, and intra- and inter-rater reliability of the objective evaluation.MethodsForty-eight trained evaluators used VERAM to evaluate visual ergonomics at 174 workstations. The time interval for test-retest and intra-rater evaluations was 2–3 weeks, and the time interval for inter-rater evaluations was 0–2 days. Test-retest reliability was assessed by intraclass correlation (ICC), the standard error of measurement (SEM) and the smallest detectable change (SDC). Intra- and inter-rater reliability were assessed with weighted kappa coefficients and absolute agreement. Systematic changes were analysed with repeated measures analyses of variance and Wilcoxon sign rank test.ResultsThe ICC of the questionnaire indices ranged from 0.69 to 0.87, while SEM ranged from 7.21 to 10.19 on a scale from 1 to 100, and SDC from 14.42 to 20.37. Intra-rater reliability of objective evaluations ranged from 0.57 to 0.85 (kappa coefficients) and the agreement from 69 to 91%. Inter-rater reliability of objective evaluations ranged from 0.37 to 0.72 (kappa coefficients) and the agreement from 52 to 87%.ConclusionVERAM is a reliable instrument for assessing risks in visual work environments. However, the reliability might increase further by improving the quality of training for evaluators. Complementary evaluations of VERAM's sensitivity to changes in the visual environment are needed.Relevance to industryIt is advantageous to set up a work environment for maximal visual comfort to avoid negative effects on work postures and movements and thus prevent visual- and musculoskeletal symptoms. This method, VERAM, satisfies the need of a valid and reliable tool for determining risks associated with the visual work environment.
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16. |
- Aronsson, Gunnar, et al.
(författare)
-
Healthy workplaces for women and men of all ages
- 2017
-
Rapport (övrigt vetenskapligt/konstnärligt)abstract
- The aim of this knowledge compilation is to contribute with knowledge about the work environment in relation to the ever-older workforce. How do employee needs and possibilities change from a course of life perspective? What should the employer and other work environment actors think about in order for the workforce to be able to and want to work to a high age?The Swedish Work Environment Authority wishes to give an overarching knowledge profile of different aspects of the work environment and the ageing workforce, and we therefore asked seven researchers to summarise the research-based knowledge within each of their areas, from a course of life and gender perspective. An eighth researcher acted as an editor for the anthology, and has also written the preface.In summary, the report shows that we are becoming even healthier, living ever longer and working to an ever higher age. Older people in the workforce are positive for the economy because productivity increases, and the business sector can make use of competent and experienced staff for a longer time. But for the older labour force to be healthy and want to work at higher ages, one needs to take into consideration how ageing influences health and the capacity to work. With age, all people are affected to different degrees by reduced vision, hearing and physical capacity, as well as longer reaction times. Even their cognitive capacity changes. Certain cognitive abilities are strengthened with rising age, while others deteriorate. With an ageing workforce, more employees have chronic illnesses, which, however, seldom affect the actual working ability. Changes in working life also affect health and wellbeing, for example deregulated work and the technical development. Age and previous experiences impact upon our ability to adapt to these changes. One factor that promotes adaptation is partly resilience (that is to say, resistance and the ability to adapt to the new), partly compensation strategies when the mental and physical resources change. There are no great differences between gender when it comes to the consequences of ageing on health and wellbeing in the work. On the other hand, the public health trend shows increasing differences in health between the lower educated and the higher educated - a difference increasing more quickly among women than among men. The gender-segregated labour market also means that more women than men work in physical and mentally burdensome work. Attitudes at the workplace also affect wellbeing and the will to continue working at higher ages. Men tend to be more sensitive to age discrimination while women run the risk of double discrimination, that is to say based upon both gender and age. Work environment and the attitude to an older workforce are central to the considerations that an employee makes in the choice between continuing to work and retiring. Other prerequisites that influence the decision are one’s own health, private finances and self-fulfilling activities.The employer can do a great deal to lengthen and improve their employees’ working life. Systematic work environment management benefits everyone, and it can contribute to everyone keeping their working ability and to older people wanting to and being able to work for longer. Occupational health services of good quality also play an important role. Technical aids and adaptation of the working pace and working tasks are other measures that improve the work environment for the older workforce. The employer can also contribute to stimulating work arrangements and organisational support for the employees in order to strengthen their resilience and promote the development of compensation strategies.
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17. |
- Bahbou, M. Fouzi, 1973-, et al.
(författare)
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A parameter study of the Protal® Process to optimise the adhesion of Ni5Al Coatings
- 2004
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Ingår i: Thermal Spray 2004 : Advances in technology and applications. - 9780871708090 ; , s. 898-902
-
Konferensbidrag (refereegranskat)abstract
- The Protal process combines surface preparation using a laser and thermal spraying in one production step. The laser preparation is based on a photomechanical reaction induced by the interaction between a laser of high instantaneous power and a polluted surface. The mechanism of bonding and the coating-substrate interface are then changed in comparison with grit blasting resulting in a significantly reduced substrate roughness. This study is aimed at finding the optimal Protal process parameters for the coating adhesion of a Ni5%Al sprayed on Ti6Al4V and IN718 alloys. The parameters investigated are laser beam intensity, the time delay between the laser impact and the spray impact, powder feed rate, substrate roughness and temperature. A test plan including these parameters is analysed by means of a fractional factorial design of experiment method. The adhesions of the coatings are measured using the ASTM C633 standard test. Data are analysed by a multiple linear regression model using a least squares fit. In addition, the coating/substrate interface is examined by optical and electron scanning microscopy (SEM) techniques as well as by Auger electron spectroscopy. Substrate roughness, substrate temperature and laser intensity are all shown to have a negative correlation with adhesion strength within the investigated range. Areas of diffusion are noticed at the coating/substrate interface.
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18. |
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19. |
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20. |
- Bahbou, M. Fouzi, 1973-, et al.
(författare)
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On-Line measurement of plasma-sprayed ni-particles during impact on a ti-surface : influence of surface oxidation
- 2007
-
Ingår i: Journal of thermal spray technology (Print). - : Springer Science and Business Media LLC. - 1059-9630 .- 1544-1016. ; 16:6, s. 506-511
-
Tidskriftsartikel (refereegranskat)abstract
- The objective of this study was to analyze the impact of plasma-sprayed Ni5%Al particles on polished and grit-blasted Ti6Al4V samples under oxidized and nonoxidized conditions. For this purpose, measurements of thermal radiation and velocity of individual plasma-sprayed particles were carried out. From the thermal radiation at impact, splat diameter during flattening and temperature evolution during cooling were evaluated. Characteristic parameters related to the quality of contact between the splat and the substrate were retrieved. The flattening speed was introduced to characterize wetting, while the cooling rate was used to characterize solidification. The idea was to get a signature of particle impact for a given surface roughness and oxidation state by identifying parameters which strongly affect the splat behavior. Sieved Ni5%Al powder in a narrow range (+65 −75 μm) was sprayed on four sets of titanium alloy surfaces, consisting of polished and grit-blasted samples, one set had a nonoxidized surface and the other one was oxidized in an oven at 600 °C for two hours. Resulting splats after impact were characterized by scanning electron microscopy, the splats on oxidized surface showed pores in their core and detached fingers at the periphery. The cooling rate and flattening degree significantly increased on the oxidized smooth surface compared to the nonoxidized one. This trend was not found in grit-blasted surfaces, which implies that impact phenomena are different on grit-blasted surfaces than on smooth surfaces thus further work is needed.
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21. |
- Bahbou, M. Fouzi, 1973-, et al.
(författare)
-
Relationship between surface topgraphy parameters and adhesion strength for plasma spraying
- 2005
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Ingår i: ITSC 2005. - : The Material Information Society. ; , s. 1027-1031
-
Konferensbidrag (refereegranskat)abstract
- To achieve sufficient adhesion strength within thermal spraying, the surface to be coated has to be modified. Grit blasting is the most common way to generate a clean and roughened surface. The bonding mechanism between the grit-blasted substrate and the coating is assumed to be due to mechanical anchoring, why an optimal surface roughness is essential. The surface roughness is usually evaluated using Ra which cannot fully characterize the complex nature of the chaotic substrate topography. This study was performed in order to evaluate if Ra can be replaced by other surface characteristic parameters such us R.q, Rpk, Rpv, Rk…with higher correlation to adhesion strength. Average roughness was measured by a perthometer and with white light interferometry to get 3D images of the surface topography. Disc shaped substrate samples of Ti6Al4V (AMS 4928) were grit blasted with aluminium oxide grit and plasma sprayed with a Ni5%Al coating. Adhesion strength was determined according to the ASTM C633 standard. The correlation between a number of different surface-parameters and adhesion strength were evaluated and compared with Ra.
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22. |
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23. |
- Balachandramurthi, Arun Ramanathan
(författare)
-
Fatigue Properties of Additively Manufactured Alloy 718
- 2018
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Additive Manufacturing (AM), commonly known as 3D Printing, is a disruptive modern manufacturing process, in which parts are manufactured in a layer-wise fashion. Among the metal AM processes, Powder Bed Fusion (PBF) technology has opened up a design space that was not formerly accessible with conventional manufacturing processes. It is, now, possible to manufacture complex geometries, such as topology-optimized structures, lattice structures and intricate internal channels, with relative ease. PBF is comprised of Electron Beam Melting (EBM) and Selective Laser Melting (SLM) processes.Though AM processes offer several advantages, the suitability of these processes to replace conventional manufacturing processes must be studied in detail; for instance, the capability to produce components of consistent quality. Therefore, understanding the relationship between the AM process together with the post treatment used and the resulting microstructure and its influence on the mechanical properties is crucial, to enable manufacturing of high-performance components. In this regard, for AM built Alloy 718, only a limited amount of work has been performed compared to conventional processes such as casting and forging. The aim of this work, therefore, is to understand how the fatigue properties of EBM and SLM built Alloy 718, subjected to different thermal post-treatments, is affected by the microstructure. In addition, the effect of as-built surface roughness is also studied.Defects can have a detrimental effect on fatigue life. Numerous factors such as the defect type, size, shape, location, distribution and nature determine the effect of defects on properties. Hot Isostatic Pressing (HIP) improves fatigue life as it leads to closure of most defects. Presence of oxides in the defects, however, hinders complete closure by HIP. Machining the as-built surface improves fatiguelife; however, for EBM manufactured material, the extent of improvement is dependent on the amount of material removed. The as-built surface roughness, which has numerous crack initiation sites, leads to lower scatter in fatigue life. In both SLM and EBM manufactured material, fatigue crack propagation is transgranular. Crack propagation is affected by grain size and texture of the material.
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24. |
- Balachandramurthi, Arun Ramanathan, 1989-
(författare)
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Towards understanding the fatigue behaviour of Alloy 718 manufactured by Powder Bed Fusion processes
- 2020
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Additive Manufacturing (AM) is a disruptive modern manufacturing process in which parts are manufactured in a layer-wise fashion. Among the metal AM processes, Powder Bed Fusion (PBF) technology — comprised of Electron Beam Powder Bed Fusion (EB-PBF) and Laser Beam Powder Bed Fusion (LB-PBF) —has opened up a design space that was formerly unavailable with conventionalmanufacturing processes. PBF processes offer several advantages; however, thesuitability of these processes to replace the conventional processes must be investigatedin detail. Therefore, understanding the AM process – post-processing –microstructure – property relationships is crucial for the manufacturing of high performance components. In this regard, only limited work has been done towards understanding the fatigue behaviour of PBF Alloy 718. The aim of this work, therefore, is to understand how the fatigue behaviour of PBF Alloy 718 is affected by its microstructure. Besides, the influence of the rough as-built surface is also investigated. In general, the <100> fibre texture along the build direction that resulted from PBF processing of Alloy 718 led to anisotropy in Young's modulus. Consequently,the fatigue performance under controlled amplitudes of strain was anisotropic such that the low-modulus direction had longer fatigue life and vice versa. This texture-induced elasticity-dependent anisotropic strain-life behaviour couldbe normalized by the pseudo-elastic stress vs fatigue life approach.Inclusions and defects had a detrimental effect on fatigue performance. Numerousfactors, such as their geometry, volume fraction, and distribution, determinedthe effect on fatigue behaviour. Hot Isostatic Pressing (HIP) eliminated most defect sand led to an improvement in fatigue performance. However, HIP did not alter the inclusions, which acted as crack initiation sites and reduced fatigue life. The rough as-built surface, which had numerous notch-like crack initiation sites, deteriorated fatigue performance; however, it lowered the scatter in fatigue life. Machining off the as-built surface improved fatigue life but increased the scatter.
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25. |
- Bolelli, G., et al.
(författare)
-
Sliding and abrasive wear behaviour of HVOF- and HVAF-sprayed Cr3C2-NiCr hardmetal coatings
- 2016
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Ingår i: Wear. - : Elsevier BV. - 0043-1648 .- 1873-2577. ; 358-359, s. 32-50
-
Tidskriftsartikel (refereegranskat)abstract
- This paper provides a comprehensive characterisation of HVOF- and HVAF-sprayed Cr3C2–25 wt.% NiCr hardmetal coatings. One commercial powder composition with two different particle size distributions was processed using five HVOF and HVAF thermal spray systems.All coatings contain less Cr3C2 than the feedstock powder, possibly due to the rebound of some Cr3C2-rich particles during high-velocity impact onto the substrate.Dry sand-rubber wheel abrasive wear testing causes both grooving and pull-out of splat fragments. Mass losses depend on inter- and intra-lamellar cohesion, being higher (≥70 mg after a wear distance of 5904 m) for the coatings deposited with the coarser feedstock powder or with one type of HVAF torch.Sliding wear at room temperature against alumina involves shallower abrasive grooving, small-scale delamination and carbide pull-outs, and it is controlled by intra-lamellar cohesion. The coatings obtained from the fine feedstock powder exhibit the lowest wear rates (≈5x10−6 mm3/(Nm)). At 400 °C, abrasive grooving dominates the sliding wear behaviour; wear rates increase by one order of magnitude but friction coefficients decrease from ≈0.7 to ≈0.5. The thermal expansion coefficient of the coatings (11.08x10−6 °C−1 in the 30–400 °C range) is sufficiently close to that of the steel substrate (14.23x10−6 °C−1) to avoid macro-cracking
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26. |
- Bolelli, G., et al.
(författare)
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Tribology of HVOF- and HVAF-sprayed WC-10Co4Cr hardmetal coatings : A comparative assessment
- 2015
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Ingår i: Surface and Coatings Technology. - : Elsevier. - 0257-8972. ; 265, s. 125-144
-
Tidskriftsartikel (refereegranskat)abstract
- his paper provides a comprehensive assessment of the sliding and abrasive wear behaviour of WC–10Co4Cr hardmetal coatings, representative of the existing state-of-the-art. A commercial feedstock powder with two different particle size distributions was sprayed onto carbon steel substrates using two HVOF and two HVAF spray processes.Mild wear rates of < 10-7 mm3/(Nm) and friction coefficients of ≈ 0.5 were obtained for all samples in ball-on-disk sliding wear tests at room temperature against Al2O3 counterparts. WC–10Co4Cr coatings definitely outperform a reference electrolytic hard chromium coating under these test conditions. Their wear mechanisms include extrusion and removal of the binder matrix, with the formation of a wavy surface morphology, and brittle cracking. The balance of such phenomena is closely related to intra-lamellar features, and rather independent of those properties (e.g. indentation fracture toughness, elastic modulus) which mainly reflect large-scale inter-lamellar cohesion, as quantitatively confirmed by a principal component analysis. Intra-lamellar dissolution of WC into the matrix indeed increases the incidence of brittle cracking, resulting in slightly higher wear rates. At 400 °C, some of the hardmetal coatings fail because of the superposition between tensile residual stresses and thermal expansion mismatch stresses (due to the difference between the thermal expansion coefficients of the steel substrate and of the hardmetal coating). Those which do not fail, on account of lower residual stresses, exhibit higher wear rates than at room temperature, due to oxidation of the WC grains.The resistance of the coatings against abrasive wear, assessed by dry sand–rubber wheel testing, is related to inter-lamellar cohesion, as proven by a principal component analysis of the collected dataset. Therefore, coatings deposited from coarse feedstock powders suffer higher wear loss than those obtained from fine powders, as brittle inter-lamellar detachment is caused by their weaker interparticle cohesion, witnessed by their systematically lower fracture toughness as well.
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27. |
- Chen, Y., et al.
(författare)
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Characterization and understanding of residual stresses in a NiCoCrAlY bond coat for thermal barrier coating application
- 2015
-
Ingår i: Acta Materialia. - : Elsevier BV. - 1359-6454 .- 1873-2453. ; 94, s. 1-14
-
Tidskriftsartikel (refereegranskat)abstract
- The residual stresses in a NiCoCrAlY bond coat deposited on a Ni-base superalloy substrate after oxidation at 1150 °C were studied by X-ray diffraction using the sin2Ψ technique. The stresses were found to be tensile; they first increased and then decreased with oxidation time. High temperature stress measurement indicated that the stress developed and built up upon cooling, predominantly within the temperature range from 1150 °C to 600 °C. Microstructural examination suggested that, due to the limited penetration depth into the bond coat, the X-ray only probed the stress in a thin surface layer consisting of the single γ-phase formed through Al depletion during oxidation. Quantitative high temperature X-ray diffraction analysis revealed that, above 600 °C, the volume fraction of the β-phase in the bond coat increased with decreasing temperature. The mechanisms of stress generation in the bond coat were examined and are discussed based on the experiments designed to isolate the contribution of possible stress generation factors. It was found that the measured bond coat stresses were mainly induced by the volume change of the bond coat associated with the precipitation of the β-phase upon cooling.
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28. |
- Chen, Ying, et al.
(författare)
-
Measurements of elastic modulus and fracture toughness of an air plasma sprayed thermal barrier coating using micro-cantilever bending
- 2019
-
Ingår i: Surface & Coatings Technology. - : Elsevier BV. - 0257-8972 .- 1879-3347. ; 374, s. 12-20
-
Tidskriftsartikel (refereegranskat)abstract
- The elastic modulus and fracture toughness of an air plasma sprayed thermal barrier coating (APS TBC) were measured using the micro-cantilever bending technique. The micro-cantilevers were machined by a focused ion beam with their central arms either parallel or normal to the bond coat/topcoat interface. Such orientations allowed direct measurements of both the in-plane and out-of-plane elastic moduli as well as mode I fracture toughness by bending. The calculated elastic modulus along the in-plane and out-of-plane direction is 144 GPa and 110 GPa, respectively, suggesting that the APS TBC is elastically anisotropic at microscale. The derived mode I fracture toughness along the plane parallel to the interface is 0.40 MPam. This relatively low toughness reflects the weak fracture resistance of the highly-flawed APS for short cracks at microscale. The measurements in this study can be incorporated into micromechanical life time prediction models of the APS TBCs. © 2019 Elsevier B.V.
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29. |
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30. |
- Clement, C., et al.
(författare)
-
Corrosion behavior of HVAF- and HVOF-sprayed high-chromium Fe-based coatings
- 2015
-
Konferensbidrag (refereegranskat)abstract
- Fe-based coatings with three particular elemental compositions and two different powder particle size were prepared by high-velocity air fuel (HVAF) and high-velocity oxy fuel (HVOF) techniques. The corrosion behavior of which were comparatively studied in 3.5 wt.% NaCl solution. The results indicated that the coatings produced by HVAF process exhibited denser structure with lower porosity. Polarization and electrochemical impedance spectroscopy (EIS) tests indicated that the HVAF coatings provided better corrosion resistance than the HVOF coatings. The presence of defects was significant in HVOF coatings. The investigation illustrated that the corrosion paths initiated and grow through defects of the coating. Furthermore, adding Cr strongly improved the corrosion resistance of the coatings. The results confirmed that the cheap HVAF process could be a potential alternative to HVOF to fabricate Fe-based coatings for industrial applications.
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31. |
- Csajbok, Ludvig Z, 1964, et al.
(författare)
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Apolipoprotein E polymorphism in aneurysmal subarachnoid haemorrhage in West Sweden.
- 2016
-
Ingår i: Acta neurologica Scandinavica. - : Hindawi Limited. - 1600-0404 .- 0001-6314. ; 133:6, s. 466-474
-
Tidskriftsartikel (refereegranskat)abstract
- Aneurysmal subarachnoid haemorrhage (aSAH) is associated with high morbidity and mortality despite novel treatments. Genetic variability may explain outcome differences. Apolipoprotein E (ApoE) is a glycoprotein with a major role in brain lipoprotein metabolism. It has three isoforms encoded by distinct alleles: APOEε2, APOEε3 and APOEε4. The APOEε4 allele is associated with Alzheimer's disease and worse outcome after traumatic brain injury and ischaemic stroke. This prospective blinded study explored the influence of the APOEε4 polymorphism on the risk of aSAH, risk of cerebral vasospasm (CVS) and 1-year neurological outcome.
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32. |
- Curry, Nicholas, 1984-
(författare)
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Design of Thermal Barrier Coating Systems
- 2012
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Thermal barrier coatings (TBC’s) are used to provide both thermal insulation and oxidation protection to high temperature components within gas turbines. The development of turbines for power generation and aviation has led to designs where the operation conditions exceed the upper limits of most conventional engineering materials. As a result there has been a drive to improve thermal barrier coatings to allow the turbine to operate hotter for longer.The focus of this study has been the development of a new generation of TBC system for industrial implementation. The goal for these new coatings was to achieve lower conductivity and longer lifetime than those coatings used today. The route taken to achieve these goals has been twofold. Firstly an alternative stabiliser has been chosen for the zirconium oxide system in the form of dysprosia. Secondly, Control of the powder morphology and spray parameters has been used to generate coating microstructures with favourable levels of porosity.Samples have been heavily characterised using the laser flash technique for evaluation of thermal properties. Measurements were performed at room temperature and at intervals up to 1200°C. Samples have also been tested in their as produced state and after heat treatments of up to 200 hours.Lifetime evaluation has been performed using the thermo-cyclic fatigue test to expose coating systems to successive cycles of heating and cooling combined with oxidation of the underlying metallic coating.Microstructures have been prepared and analysed using SEM. An image analysis routine has been used to attempt to quantify changes in microstructure features between coating types or coating exposure times and to relate those changes to changes in thermal propertiesResults show that dysprosia as an alternative dopant gives a reduction in thermal conductivity. While small at room temperature and in the as produced state; the influence becomes more pronounced at high temperatures and with thermal exposure time. Overall, the greatest sustained influence on thermal conductivity has been from creating coatings with high levels of porosity.In relation to lifetime, the target of double the thermo-cyclic fatigue life was achieved using a coating with engineered porosity. Introducing a polymer to the spray powder helps to generate large globular pores within the coating together with a large number of delaminations. Such a structure has shown to be highly resistant to TCF testing.
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33. |
- Curry, Nicholas, 1984-
(författare)
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Design of Thermal Barrier Coatings
- 2014
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Thermal barrier coatings (TBC’s) are used to provide both thermal insulation and oxidation protection to high temperature components within gas turbines. The development of turbines for power generation and aviation has led to designs where the operation conditions exceed the upper limits of most conventional engineering materials. As a result there has been a drive to improve thermal barrier coatings to allow the turbine to operate at higher temperatures for longer.The focus of this thesis has been to design thermal barrier coatings with lower conductivity and longer lifetime than those coatings used in industry today. The work has been divided between the development of new generation air plasma spray (APS) TBC coatings for industrial gas turbines and the development of suspension plasma spray (SPS) TBC systems.The route taken to achieve these goals with APS TBC’s has been twofold. Firstly an alternative stabiliser has been chosen for the zirconium oxide system in the form of dysprosia. Secondly, control of the powder morphology and spray parameters has been used to generate coating microstructures with favourable levels of porosity.In terms of development of SPS TBC systems, these coatings are relatively new with many of the critical coating parameters not yet known. The focus of the work has therefore been to characterise their lifetime and thermal properties when produced in a complete TBC system.Results demonstrate that dysprosia as an alternative stabiliser gives a reduction in thermal conductivity. While small at room temperature and in the as produced state; the influence becomes more pronounced at high temperatures and with longer thermal exposure time. The trade-off for this lowered thermal conductivity may be in the loss of high temperature stability. Overall, the greatest sustained influence on thermal conductivity has been from creating coatings with high levelsof porosity.In relation to lifetime, double the thermo-cyclic fatigue (TCF) life relative to the industrial standard was achieved using a coating with engineered porosity. Introducing a polymer to the spray powder helps to generate large globular pores within the coating together with a large number of delaminations. Such a structure was shown to be highly resistant to TCF testing.SPS TBC’s were shown to have much greater performance relative to their APS counterparts in thermal shock life, TCF life and thermal conductivity. Columnar SPS coatings are a prospective alternative for strain tolerant coatings in gas turbine engines.
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34. |
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35. |
- Ericsson, Mikael, 1975-, et al.
(författare)
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A look at the optimization of robot welding speed based on process modelling
- 2007
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Ingår i: Welding Journal. - 0043-2296. ; 86:8, s. 238-244
-
Tidskriftsartikel (refereegranskat)abstract
- Simulation tools to search for optimal process parameters are of great interest to reduce the number of experiments and thereby reduce cost and production time. In this paper, robot simulation has been used in combination with finite element simulations to optimize robot speed in order to minimize distortion while keeping complete joint penetration. In an earlier work performed by the authors, a finite element model was developed to predict heat transfer and residual stresses of parts with complex shapes. An interface between a robot simulation model and a finite element analysis model was also constructed. In this paper, an iterative method for robot speed optimization has been developed using MATLAB. The algorithm is designed to maintain complete joint penetration while maximizing productivity by utilizing the fastest weld speed. The method makes it possible to optimize the heat input to the component and thereby minimize component deformation for parts with complex shapes. The system was evaluated on stainless steel plates with varying thicknesses. Robot weld paths were defined off line and automatically downloaded to the finite element software where the optimization was performed. Simulations and experimental validations are presented.
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36. |
- Ericsson, Mikael, 1975-, et al.
(författare)
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Off-line programming of robots for metal deposition
- 2005
-
Ingår i: Trends in welding research. - 0871708426 ; , s. 629-634
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Metal Deposition (MD) is a rapid prototyping technique to build parts by depositing metal in a required fashion. When a complex-shaped part is to be built, a simulation tool is needed to define robot trajectories. Three different simulation-based methods for robot trajectory generation are introduced and compared in this study. The methods are; reversed milling, adapted rapid prototyping and application programming in a computer aided robotics software. All methods were shown capable of creating robot paths for complex shapes, with the CAR software approach being the most flexible. Using this method, the geometry to be built is automatically sliced into layers and a robot path is automatically generated. The method was tentatively evaluated and appears to provide a powerful technique in the design and optimisation of robot paths for MD. Experiments showed that it is possible to manufacture fully dense parts using an Nd-Yag laser.
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37. |
- Ericsson, Mikael, 1975-, et al.
(författare)
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Three-dimensional simulation of robot path and heat transfer of a TIG-welded part with complex geometry
- 2002
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Ingår i: 11th International Conferences on Computer Technology in Welding. - : Society of Manufacturing Engineers, North American Manufacturing Research Institution. ; , s. 309-316
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- The application of commercial software (OLP) packages for robot simulation, and programming, use interactive computer graphics, provide powerful tools for creating welding paths off-line. By the use of such software, problems of robot reach, accessibility, collision and timing can be eliminated during the planning stage. This paper describes how such software can be integrated with a numerical model that predicts temperature-time histories in the solid material. The objective of this integration is to develop a tool for the engineer where robot trajectories and process parameters can be optimized on parts with complex geometry. Such a tool would decrease the number of weld trials, increase productivity and reduce costs. Assumptions and principles behind the modeling techniques are presented together with experimental evaluation of the correlation between modeled and measured temperatures.
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38. |
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39. |
- Ericsson, Mikael, 1975-, et al.
(författare)
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Three Dimensional Simulation of Robot path, Heat Transfer and Residual Stresses of a TIG-welded Part with Complex Geometry
- 2002
-
Ingår i: Trends in Welding Research: Proceedings of the 6th International Conference. ; , s. 973-978
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- In this paper a system is presented that combines a robot off-line programming software with a finite element model that predicts temperature-time histories and residual stress distributions. The objective is to develop a tool for the engineer where robot trajectories and welding process parameters can be optimized on parts with complex geometry. The system was evaluated on a stainless steel gas turbine component. Robot weld paths were defined off-line and automatically downloaded to the finite element program, where transient temperatures and residual stresses were predicted. Temperature dependent properties and phase change, were included in the analysis. Assumptions and principles behind the modeling techniques are presented together with predicted temperature histories, residual stresses, and fixture forces.
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40. |
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41. |
- Ericsson, Mikael, 1975-, et al.
(författare)
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Three dimensional simulation of robot path, heat transfer and residual stresses of a welded part with complex geometry
- 2005
-
Ingår i: International jourrnal for the joining of materials. - 0905-6866. ; 17:2, s. 42-51
-
Tidskriftsartikel (refereegranskat)abstract
- In this article a simulation system is presented that combines computer aided robotics software used to define the welding operation, with a finite element model that predicts temperature-time histories and residual stress distributions for welding applications. The objective is to develop a tool for engineering processes in which robot trajectories and welding process parameters can be optimized off-line on parts with complex geometries. The system was evaluated on a stainless steel gas turbine component. Temperature dependent properties and phase change were included in the analysis. The turbine component was welded using an in-house TIG welding cell. The assumptions and principles that underpin the modeling techniques are presented together with predicted temperature histories, residual stresses, and fixture forces. Predicted residual stresses were compared with neutron diffraction measurements.
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42. |
- Eriksson, Robert, et al.
(författare)
-
Stresses and Cracking During Chromia-Spinel-NiO Cluster Formation in TBC Systems
- 2015
-
Ingår i: Journal of thermal spray technology (Print). - : Springer Science and Business Media LLC. - 1059-9630 .- 1544-1016. ; 24:6, s. 1002-1014
-
Tidskriftsartikel (refereegranskat)abstract
- Thermal barrier coatings (TBC) are used in gas turbines to reduce the temperatures in the underlying substrate. There are several mechanisms that may cause the TBC to fail; one of them is cracking in the coating interface due to extensive oxidation. In the present study, the role of so called chromia-spinel-NiO (CSN) clusters in TBC failure was studied. Such clusters have previously been found to be prone to cracking. Finite element modeling was performed on a CSN cluster to find out at which stage of its formation it cracks and what the driving mechanisms of cracking are. The geometry of a cluster was obtained from micrographs and modeled as close as possible. Nanoindentation was performed on the cluster to get the correct Youngâs moduli. The volumetric expansion associated with the formation of NiO was also included. It was found that the cracking of the CSN clusters is likely to occur during its last stage of formation as the last Ni-rich core oxidizes. Furthermore, it was shown that the volumetric expansion associated with the oxidation only plays a minor role and that the main reason for cracking is the high coefficient of thermal expansion of NiO. © 2015 ASM International
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43. |
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44. |
- Fasth, Angelica, et al.
(författare)
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A comparative study of mechanical properties between HVOF-sprayed Maxphase materials
- 2009
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Ingår i: Proceedings of the 22nd International Conference on Surface Modification Techniques. - 9780981706511 ; , s. 149-156
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Konferensbidrag (refereegranskat)abstract
- Mn+1AXn –phases (MAX-phase materials) are ternary compounds consisting of an early transition metal (M), such as Ti or V, a p-element from group III-V (A) and C and/or N (X). The phases have a layered structure in which the A element form planes separated by MX slabs. This nanolaminated atomic arrangement gives rise to a unique set of properties. These properties in combination with a good match in thermal expansion between substrate and coating make MAX-phase materials challenging materials to extend the lifetime of thermal barrier coatings. Evaluation of properties of HVOF sprayed MAX-phase materials and to compare these properties with commercially used bond coat materials such as MCrAlY coatings is thus of great interest which was the aim of this study.The non-linear load displacement relationships and Young’s modulus for HVOF-sprayed Ti2AlC coatings and APSsprayed NiCoCrAlY coatings onto Hastalloy X substrates were determined using data from both Berkovich andspherical microindentation. Results between Berkovich and spherical microindentation measurements are comparedand discussed.
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45. |
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46. |
- Fu, Qilin, 1986-
(författare)
-
High dynamic stiffness nano-structured composites for vibration control : A Study of applications in joint interfaces and machining systems
- 2015
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Vibration control requires high dynamic stiffness in mechanical structures for a reliable performance under extreme conditions. Dynamic stiffness composes the parameters of stiffness (K) and damping (η) that are usually in a trade-off relationship. This thesis study aims to break the trade-off relationship.After identifying the underlying mechanism of damping in composite materials and joint interfaces, this thesis studies the deposition technique and physical characteristics of nano-structured HDS (high dynamic stiffness) composite thick-layer coatings. The HDS composite were created by enlarging the internal grain boundary surface area through reduced grain size in nano scale (≤ 40 nm). The deposition process utilizes a PECVD (Plasma Enhanced Chemical Vapour Deposition) method combined with the HiPIMS (High Power Impulse Magnetron Sputtering) technology. The HDS composite exhibited significantly higher surface hardness and higher elastic modulus compared to Poly(methyl methacrylate) (PMMA), yet similar damping property. The HDS composites successfully realized vibration control of cutting tools while applied in their clamping interfaces.Compression preload at essential joint interfaces was found to play a major role in stability of cutting processes and a method was provided for characterizing joint interface properties directly on assembled structures. The detailed analysis of a build-up structure showed that the vibrational mode energy is shifted by varying the joint interface’s compression preload. In a build-up structure, the location shift of vibration mode’s strain energy affects the dynamic responses together with the stiffness and damping properties of joint interfaces.The thesis demonstrates that it is possible to achieve high stiffness and high damping simultaneously in materials and structures. Analysis of the vibrational strain energy distribution was found essential for the success of vibration control.
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47. |
- Ganvir, Ashish, 1991-, et al.
(författare)
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Characterization of Microstructure and Thermal Properties of YSZ Coatings Obtained by Axial Suspension Plasma Spraying (ASPS)
- 2015
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Ingår i: Journal of thermal spray technology (Print). - : Springer Science and Business Media LLC. - 1059-9630 .- 1544-1016. ; 24:7, s. 1195-1204
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Tidskriftsartikel (refereegranskat)abstract
- The paper aims at demonstrating various microstructures which can be obtained using the suspension spraying technique and their respective significance in enhancing the thermal insulation property of a thermal barrier coating. Three different types of coating microstructures are discussed which were produced by the Axial Suspension Plasma Spraying. Detailed characterization of coatings was then performed. Optical and scanning electron microscopy were utilized for microstructure evaluations; x-ray diffraction for phase analysis; water impregnation, image analysis, and mercury intrusion porosimetry for porosity analysis, and laser flash analysis for thermal diffusivity measurements were used. The results showed that Axial Suspension Plasma Spraying can generate vertically cracked, porous, and feathery columnar-type microstructures. Pore size distribution was found in micron, submicron, and nanometer range. Higher overall porosity, the lower density of vertical cracks or inter-column spacing, and higher inter-pass porosity favored thermal insulation property of the coating. Significant increase in thermal diffusivity and conductivity was found at higher temperature, which is believed to be due to the pore rearrangement (sintering and pore coarsening). Thermal conductivity values for these coatings were also compared with electron beam physical vapor deposition (EBPVD) thermal barrier coatings from the literature and found to be much lower. © 2015 ASM International
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48. |
- Ganvir, Ashish, 1991-, et al.
(författare)
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Comparative study of suspension plasma sprayed and suspension high velocity oxy-fuel sprayed YSZ thermal barrier coatings
- 2015
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Ingår i: Surface and Coatings Technology. - : Elsevier. - 0257-8972. ; 268, s. 70-76
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Tidskriftsartikel (refereegranskat)abstract
- Suspension Thermal Spraying is a relatively new thermal spaying technique to produce advanced thermal barrier coatings. This technique enables the production of much different performance thermal barrier coatings than conventional thermal spraying which uses solid powder as a feedstock material. In this work a comparative study is performed on four different types of thermal barrier coatings sprayed with two different thermal spay processes, suspension high velocity oxy-fuel spraying (SHVOF) and suspension plasma spraying (SPS) using two different water-based suspensions. Tests carried out include microstructural analysis with SEM, porosity analysis using weight difference by water infiltration, thermal conductivity measurements using laser flash analysis and lifetime assessment using thermo-cyclic fatigue tests. The results showed that SPS coatings were much porous and hence showed lower thermal conductivity than SHVOF coatings produced with the same suspension. From the thermo-cycling tests it was observed that the SPS coatings showed a higher lifetime than the SHVOF ones.
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49. |
- Ganvir, Ashish, 1991-
(författare)
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Design of Suspension Plasma Sprayed Thermal Barrier Coatings
- 2018
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Thermal barrier coatings (TBCs) are widely used on gas turbine components to provide thermal insulation, which in combination with advanced cooling, can enable the gas turbine to operate at significantly higher temperatures even above the melting temperature of the metallic components. There is a permanent need,mainly due to environmental reasons, to increase the combustion temperature inturbines, hence new TBC solutions are needed. By using a liquid feedstock in thermal spraying, new types of TBCs can be produced. Suspension plasma/flame or solution precursor plasma spraying are examples of techniques that can be utilized for liquid feedstock thermal spraying. This approach of using suspension and solution feedstock, which is an alternative to the conventional solid powder feedstock spraying, is gaining increasing research interest since it has been shown to be capable of producing coatings withsuperior performance. The objective of this research work was to identify relationships between process parameters, coating microstructure, thermal conductivity and lifetime in suspension plasma sprayed TBCs. A further objective was to utilize these relationships to enable tailoring of the TBC microstructure for superior performance compared to state-of-the-art TBC used in industry today, i.e. solid feedstock plasma sprayed TBCs. Different spraying techniques, namely suspension high velocity oxy fuel, solution precursor plasma and suspension plasma spraying (with axial and radial feeding) were explored and compared to solid feedstock plasma spraying. A variety of microstructures, such as highly porous, vertically cracked and columnar, were produced and investigated. It was shown that there are strong relationships between microstructure, thermo-mechanical properties and performance of the coatings. Specifically, axial suspension plasma spraying wasshown as a very promising technique to produce various microstructures as wellas highly durable coatings. Based on the experimental results, a tailored columnar microstructure design for a superior TBC performance is also proposed.
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50. |
- Ganvir, Ashish, 1991-, et al.
(författare)
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Influence of Microstructure on Thermal Properties of Axial Suspension Plasma-Sprayed YSZ Thermal Barrier Coatings
- 2016
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Ingår i: Journal of thermal spray technology (Print). - : Springer Science and Business Media LLC. - 1059-9630 .- 1544-1016. ; 25:1-2, s. 202-212
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Tidskriftsartikel (refereegranskat)abstract
- Suspension plasma spraying is a relatively new thermal spaying technique to produce advanced thermal barrier coatings (TBCs) and enables production of coatings with a variety of structures—highly dense, highly porous, segmented, or columnar. This work investigates suspension plasma-sprayed TBCs produced using axial injection with different process parameters. The influence of coating microstructure on thermal properties was of specific interest. Tests carried out included microstructural analysis, phase analysis, determination of porosity, and pore size distribution, as well as thermal diffusivity/conductivity measurements. Results showed that axial suspension plasma spraying process makes it possible to produce various columnar-type coatings under different processing conditions. Significant influence of microstructural features on thermal properties of the coatings was noted. In particular, the process parameter-dependent microstructural attributes, such as porosity, column density, and crystallite size, were shown to govern the thermal diffusivity and thermal conductivity of the coating.
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